Immunodominance of the VH1-46 antibody gene segment in the primary repertoire of human rotavirus-specific B cells is reduced in the memory compartment through somatic mutation of nondominant clones

Detailed characterization of Ag-specific naive and memory B cell Ab repertoires elucidates the molecular basis for the generation of Ab diversity and the optimization of Ab structures that bind microbial Ags. In this study, we analyzed the immunophenotype and V(H) gene repertoire of rotavirus (RV) VP6-specific B cells in three circulating naive or memory B cell subsets (CD19(+)IgD(+)CD27(-), CD19(+)IgD(+)CD27(+), or CD19(+)IgD(-)CD27(+)) at the single-cell level. We aimed to investigate the influence of antigenic exposure on the molecular features of the two RV-specific memory B cell subsets. We found an increased frequency of CD19(+)IgD(+)CD27(+) unclass-switched memory B cells and a low frequency of somatic mutations in CD19(+)IgD(-)CD27(+) class-switched memory B cells in RV-specific memory B cells, suggesting a reduced frequency of isotype switching and somatic mutation in RV VP6-specific memory B cells compared with other memory B cells. Furthermore, we found that dominance of the V(H)1-46 gene segment was a prominent feature in the V(H) gene repertoire of RV VP6-specific naive B cells, but this dominance was reduced in memory B cells. Increased diversity in the V(H) gene repertoire of the two memory B cell groups derived from broader usage of V(H) gene segments, increased junctional diversity that was introduced by differential TdT activities, and somatic hypermutation.